// write your code here
import java.util.Scanner;

//变形斐波那契
public class Main{
    
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            long[] arr = new long[91]; //这里使用long
            arr[1] = 1;
            arr[2] = 2;
            for(int i = 3; i < 91; i++){
                arr[i] = arr[i-1] + arr[i-2];
            }
            int n = sc.nextInt();
            System.out.println(arr[n]);
        }
        sc.close();
    }
    
    
}